Artificial leathers are generally composed of the combination of a nonwoven fabric and an elastic polymer and combine an appearance, flexibility and softness comparable to those of natural leathers and mechanical properties superior to those of natural leathers. Known artificial leathers are excellent in the flexibility and softness, but fail to simultaneously satisfy a high shape stability which is required, for example, in upholsteries for seats. Therefore, various methods for reinforcing the structure of nonwoven fabric with a scrim have been proposed when particularly high shape stability is needed.
The methods for reinforcing nonwoven fabrics with a scrim are roughly classified to two types: a method of uniting a scrim on one surface of a nonwoven fabric or between two nonwoven fabrics by a adhesive and a method of uniting a scrim on one surface of a nonwoven fabric or between two nonwoven fabrics by a fiber entanglement. In the former method, a scrim having desired properties is simply adhesively bonded to the back surface of, for example, a general artificial leather mentioned above. Therefore, this method can be easily performed without difficulty only by controlling the elongation of two sheet materials during the adhesion operation. The same may be said of adhesively uniting a scrim between two artificial leathers. In the latter method, a non woven fabric and a scrim, which are quite different in their fibrous structures, are united by the entanglement in the thickness direction caused by mechanically treating the fibers of the nonwoven fabric. However, this method involves several problems, because the method inevitably causes the undesirable change and damage in the structures of nonwoven fabric and scrim and the damage of fibers when the nonwoven fabric and the scrim are strongly entangled. In case of uniting a scrim with a short fiber or long fiber nonwoven fabric which is made of superfine fiber-forming fibers such as sea-island fibers and core-sheath fibers or direct-spun superfine fibers, the entanglement is generally effected by a jet flow or needle punch from the side of the nonwoven fabric of a stack which includes two sheets of nonwoven fabric and a scrim interposed between the nonwoven fabrics or a stack which includes one sheet of nonwoven fabric and a scrim superposed on one surface of the nonwoven fabric. To solve the above problems in the mechanical entanglement, there is proposed a method in which a stack of a web and a knitted or woven fabric is needle-punched using needles having a total barb depth which is half or less of the diameter of the yarns constituting the knitted or woven fabric (for example, Patent Document 1). However, the entangling efficiency of the fibers constituting the web is insufficient because the total barb depth is relatively small. To enhance the entanglement, the number of punch should be increased. However, this causes the increased damage of the knitted or woven fabric. In particular, the damage of the knitted or woven fabric becomes significant when the yarns constituting the knitted or woven fabric have a relatively small number of twists and are easily caught on barbs even when its total barb depth is small. If the number of twists is increased to solve this problem, the yarns becomes difficult to be caught on barbs and the damage of knitted or woven fabric is decreased because the highly twisted yarns are difficult to break even when caught on barbs. However, the highly twisted yarns make the feel of the knitted or woven fabric hard, this resulting in a hard feel of the resultant artificial leather. In another proposal, a fibrous sheet made of short fibers having a fiber length of 10 mm or less and a knitted or woven fabric is united by a jet flow (for example, Patent Document 2). As compared with the entanglement by needle punching, the jet flow can entangle fibers with little damage of fibers. However, since the fiber length is very short, the short fibers are likely to pull out from the united body whatever strongly entangled. Therefore, it is difficult to attain a high surface abrasion resistance without impairing the feel and appearance. In the application requiring a shape stability, which is one of the main objects of the present invention, including interior materials such as upholsteries for seats, a high surface abrasion resistance is required in addition to a feel with flexibility, softness and bulkiness. However, the production method for producing a substrate for artificial leather which sufficiently combines such properties is hitherto not proposed.
Patent Document 1: JP 7-13344B
Patent Document 2: JP 60-29775B